Wheatstone bridge relay arrangement



y 1939- T. A. COHEN 2,164,701

WHEATSTONE BRIDGE RELAY ARRANGEMENT Filed Nov. 16. 1934 5 Sheets-Sheet lJib,

INVENTOR. 77:0097: 4 604:7;

ATTORNEY.

y 4, 1939- T. A. COHEN 2,164,701

WHEATSTONE BRIDGE RELAY ARRANGEMENT Filed Nov. 16, 1934 5 Sheets-Sheet 2INVENTOR- flee 9 12. yc fiz'.

UMW M ATTORNEY.

Jill 4, 1939. I A, HEN 2,164,701

WHEATSTONE BRIDGE RELAY ARRANGEMENT Filed Nov. 16, 1934 5 Sheets-Sheet 3174 1&5

INVENT OR.

BY Then/d re 4-6 5 $6 747, MM

ATTORNEY.

July 1939- 'r. A, COHEN 2,164,701

STONE BRIDGE RELAY ARI; NGEIENT Filed Nov. 16, 1 934 5 Sheets-Sheet 4 IINVENTOR.

BY 7725040 re fg/mi. M Z/M ATTORNEY.

. y 4, 1939- T. A. COHEN 2,164,701

WHEA'I'STONE BRIDGE RELAY ARRANGEMENT Filed Nov. 16, 1934 5 Sheets-Sheet5 INVENTOR. TEOdOTE/f, Q31. Q n

ATTORNEY.

Patented July 4, 1939 UNITED STATES PATENT OFFICE WHEATSTONE BRIDGERELAY ARRANGEMENT Theodore A. Cohen, Chicago, Ill., assignor to WheelcoVacuum Products Company, a corporation of Illinois This inventionrelates to control apparatus in general and more particularly to such anapparatus as is adapted to control variable physical quantities such astemperature, pressure, speed,

light, power, phase angle and impedance, etc.

The primary object of this invention is to provide an apparatus forcontrolling such quantities with a maximum of precision.

Other and further objects of this invention will in be apparent as thesame becomes better understood from an examination of the specificationand claims in conjunction with the accompanying drawings wherein:

Fig. l is a schematic view showing a form of l the apparatus;

Fig. 2 is a similar view 01 a modification;

Fig. 3 is a similar view of another modification;

Fig. 4 is a similar view of another modification;

Fig. 5 is a schematic view of the bridge circult of Fig. 4;

Fig. 6 is a schematic view of a modification; Fig. 7 is a detailedisometric view of a variable impedance element and circuit thereforwhere temperature control is desired;

Fig. 8 is. a similar view of a modification of I Fig. 7;

Fig. 9 is a detailed fragmentary schematic view; of a variable impedancedevice adapted to be used in the apparatus in lieu of the element shownin Fig. '7 for speed control;

Fig. 10 is a similar view of another element adapted to be. used in theapparatus in lieu oi.

the element shown in Fig. 7 when light control is desired;

Fig. 11 is a similar view of another element adapted to be used in theapparatus in lieu of the element shown in Fig. 7 when pressure con- 40trol is desired;

Fig. 12 is a similar view of another element adapted to be used in theapparatus in lieu of the element shown in Fig. 'l'when power control isdesired;

45 Fig. 13 is a similar view oi another element adapted .to be used inthe apparatus in lieu of the element shown in Fig. 7 when phase anglecontrol is desired; v I

Fig. 14 is a similar viewof another element 50 adapted to be used in theapparatus in lieu of the element shown in Fig. 7 when impedance controlis desired.

Referring to the drawings more particularly reference characters I and 2represent opposite arms 55 of a Wheatstone bridge capable of beingdiiierentially set by a slider 3 and forming therewith a potentiometer.These resistances l and 2 are connected with a variable impedance 4which forms a third arm of the Wheatstone bridge and a series ofvariable and fixed resistances Iorming- 5 the fourth arm thereof. Theselatter resistances include a variable resistance 5, a variableresistance E and a fixed resistance 1. Resistance 1 is designed to beapproximately equal in value to the resistance 4 with bridgebalanced'and re- 10 sistor 4 set at balance for reference measurementsuch as room temperature. Variable resistance 5 may be adjusted tocompensate for external efiects such as sub-normal or abnormal roomtemperature, etc. Variable resistance 6 may be 16 adjusted to compensatefor the leads to the resistance 4.

The variable resistance of impedance 4 may.

; take several forms depending upon the quantity desired to becontrolled.- This variable impedgo ance 4, when temperature is desiredto be controlled may take the form of either of the elements shown inFigs. 7 and 8 which will be described more in detail hereinafter. Whenthe quantity desired to be controlled is speed, light, 25 pressure,power, phase angle, or impedance, this member 4 may take the form of theimpedance members shown in Figs. 9, 10, ll, 12, 13 or 14, respectively,as will be more particularly described hereinafter. so

The slider 3 is connected to one end of the winding of a relay 8 and thejunction point 9 of resistances 4 and 5 is connected to the other end ofsaid relay. When the potential supplied to the bridge by a battery I0 isunbalanced by predetermined variation'oi' element 4, the relay switch Hcloses the grid'circuit of a tube l2 causing a grid bias battery IS in ano-current grid circuit to put a negative potential on the grid of tubeI2 and thereby reduce the plate 40 current of the tube sufllciently torelease switch I4 normally closed by a relay l5 in the plate circuit.When the relay switch I4 is released, contact I6 is opened, cutting outcircuit connected to points I1 and J8. When the apparatus is used tocontrol temperature the bridge is balanced with the element 4 cold. Thiselement 4 being situated at the point the temperature of which isdesired to be controlled, when the temperature reaches the point wherethe decreased I resistance (if negative temperature coemcient resistortype is used) or increased resistance (if positive temperaturecoefllcient resistor type is used) in the arm 01 the bridge containingsaid element causes the closing of switch H and re-, 56

leasing of switch I4, heating coils 61 and current source 68 connectedacross points I1 and I8 will be cut out thereby causing lowering oftemperature below control point. When the resistance of element 4increasesby drop in temperature switch II will re-open and switch M willreclose circuit containing the heating coils 61 and current source 68.

In Fig. 7 the variable element 4e used in place of element 4 whencontrolling temperature is shown as coiled filaments 25 and 26differentially wound about a core formed of a pair of longitudinallyextending strips of heat proof material disposed at right angles to eachother. This arrangement permits heat currents to circulate freelythroughout the various coils. The filaments 25 and 26 are in the form ofa pair of coils wound simultaneously and insulated from each otheronehaving a positive temperature coefiicient and the other a negativetemperature coefficient respectively. The filament 26 having thenegative temperature coeflicient is connected in the circuit as shown inFig. '7 so as to be in the opposite arms of the bridge to that of thefilament having the positive temperature coeflicient whereby the elementas a whole may act to differentially unbalance the bridge in accordancewith temperature changes. Parts Ie, 2e, 5e, 6e, and 8e through I8e,inclusive, are similar to corresponding parts I, 2, 5, 6, and 8 through.I8, inclusive, respectively, in Fig. 1. Likewise parts 3e, 61c, and 68eare similar to parts 3, 6'! and 68, respectively, of Fig. 1.

As shown in Fig. 8 the variableelement 4f adapted to be used in place ofthe element .4 where temperature quantities are desired to be controlledmay take a somewhat different form. In this modification the twofilaments here designated 25) and 26), in themselves having positive andnegative temperature coefficients, respectively, may be simultaneouslystrung rather than wound upon a flat heat resisting and electricallyinsulated frame. The other parts of the apparatus are identical withcorresponding parts in Fig. 7. ,For example, parts I f, 2f and so forth,

1 through 68], correspond to similar parts Ie, 2e,

replace the element 4.

As shown in Fig. 11 when it is desired to control pressure quantities, adiaphragm 32 mounted in a fiow tube 32 in the pressure circuit isprovided with a carbon button 34, the resistance of which varies inaccordance with the pressure upon the diaphragm and this button 34- isadapted to be inserted in the circuit in place of the element 4.

As shown in Fig. 12 when it is desired to control power quantities avariable resistance 35 is substituted'for. the element 4. Thisresistance 35 is varied by a slider 36- actuated by watt meter elements31 and 38 connected in a power line, the power of which is desired to becontrolled.

v When it is desired to control phase angle quantities, a resistance 39may be substituted for the element 4. This resistance 39 (Fig. 13)

may be varied by a slider 40 actuated by y amometer elements 4| and 42.

These elements 4| and 42 are adapted to be shunted across a capacitiveinductive network 55-56, the latter being adapted to be placed in thecircuit being measured. Dynamometer elements and 42 measure,respectively, the voltage components across the capacitive reactance 56and inductive reactance 55, the total torque being proportional to phaseangle and positioning slider 40 to vary impedance element 39.

When it is desired to control impedance, im-

pedance 43 (Fig. 14) may be substituted for the element 4, terminals 44and 45 connected across said network being connected in the circuitWhere the element 4 was taken out.

In Fig. 2 a form of apparatus similar to that of Fig. 1 is shown exceptthat here the filament of the tube I2a is'energized from an alternatingcurrent line through contacts 20 and 2 I, a resistance 22 providing thenecessary drop in voltage and the relay I5a being also connected to saidline. Parts Ia, 2a and so forth, through 68a, correspond to similarparts I, 2, and so forth, through 68, in Fig.1.

When speed is being controlled instead of placing heating coils referredto in connection with Fig. 1 across points I1 and I8, a motor (notshown) controlling a steam valve or other means (not shown) for reducingthe speed might be placed thereacross. When light is being controlledsuitable means (not shown) for reducing the light intensity might beplaced across points I1 and I8. When pressure is being controlledsuitable means such as a motor (not shown) controlling a pressure pumpmight be placed across these points I1 and I8. When power is beingcontrolled suitable means (not shown) for throwing compensatinginductance in the power line might be provided across the points I! andI8. When phase angle or impedance is being controlled suitable means forthrowing compensating impedance in the line may be provided across thepoints I1 and I8.

As shown in Fig. 3, the bridge circuit containing variable contactimpedance 4b may have its potential supplied from the secondary of atransformer 46, the primary of which is connected to an alternatingcurrent source. Variable condensers 41 and 46 take the place of thepotentiometer in the previous embodiment. The secondary of thetransformer 46 also energizes the winding of a galvanometer 49, thearmature winding 50 of which is connected across the bridge. When thebridge is unbalanced the galvanometer armature is actuated to open orclose a switch 5| operable therewith to disconnect or connect contactpoints Ilb and I8b, respectively comparable to points I1 and I8 of thefirst embodiment. Parts 5b to 1b, 61b and 68b correspond to similarparts 5 to I, 61 and 68, respectively, in Fig. 1.

As shown in Fig. 4, a modified form of apparatus includes a galvanometerhaving a permanent magnet 53 and a difierentially wound armature 54 inthe bridge circuit. The armature windings include coils 55 and 56 whichare oppositely wound and take the place of resistances I and 2respectively in the firsf embodiment. A battery 51 supplies thepotential to the bridge. When the resistance of element 4c which iscomparable to element 4 is decreased, the armature 54- will be actuatedto close switch 59 operable therewith cutting in grid bias 60- anddecreasing current in plate circuit of a tube 6| releasing iii relay.and switch opening points Na and llb as-in first embodiment. Fig. 5shows the analogy oi. circuit to a bridge circuit. Parts c to lo,- 610and 68c, correspond to similar parts i to I, 61 and 68, respectively. inFig. l.

The apparatus of FigL-"G is similar to that 0! Fig. 4 -just describedexcept that an alternating current source is connected to points 63 andM for energizing a transformer 65, secondary coils of which supplyenergy for winding '0 0! galvanometer, filament of tube ilmand relay "acomparable to relay 62. Except for the foregoing, the apparatus of Fig.6 operates substantially the same as that of Fig. 4. Parts Id to Id, "dand 68d, correspond to similar parts I to I, 61 and 68, in Fig. 1. g

The operation and advantages of the aforedescribed apparatus should beapparent without further detail. 4

. I am aware that many changes may be made without departing from thespirit of this invention and I therefore do. not wish to be limited tothe details shown or described.

I claim:

1. In an apparatus 0! the character described,

a bridge circuit, a galvanometer having oppositely wound armature coilsin opposite arms of the bridge circuit, a variable impedance element ina third arm and a balancing element opposed thereto in a fourth arm, anda control circuit operable by said gaivanometer when said variableelement has been varied a predetermined amount.

2. In an apparatus of the character described, a bridge circuit, agalvanometer having oppositely wound armature coils in opposite arms ofsaid bridge, a vacuum tube grid circuit adapted to be closed when saidgalvanometer is actuated and a plate circuit adapted to have its currentreduced when said grid circuit is closed.

3. In an apparatus of the character described, a bridge circuit, agalvanometer having oppositely wound armature coils in opposite arms ofsaid bridge, a vacuum tube grid circuit adapted to be closed when saidgalvanometer is actuated and a plate circuit adapted to have its currentreduced when said grid circuit is closed and means for energizing thegalvanometer field and the plate circuit from an alternating currentsource.

THEODORE A. COHEN.

